The Eurasian curlew's bill can exceed ten centimetres in females and is driven deep into soft sediment in search of lugworms, ragworms and burrowing crustaceans. Opening a long bill against packed mud would be mechanically hopeless, so waders of this kind use rhynchokinesis: the upper mandible bends upward near the tip while the rest of the bill stays closed.
The tip is also densely supplied with sensory receptors, including Herbst corpuscles in pits in the bone, which detect pressure changes as the bill moves through wet sediment. That lets a probing bird locate buried prey it cannot see or touch directly, by sensing how the disturbance pattern in interstitial water is interrupted.
A visible consequence is that female curlews, with longer bills, tend to probe deeper than males, so the sexes partition the same mudflat. The decline of the species is not driven by feeding, though. Breeding failure on agricultural and upland grassland, through mowing, drainage and predation of nests, is the main pressure, and how to reverse it at landscape scale is unsettled.